A diver explores a reef with rare ellk horn coarl in John Pennekamp state park in Key Largo.

Out on Carysfort, Molasses, Hens and Chickens reefs off the Keys, the boulder, brain and fire corals are starting to rebound from the latest bout of bleaching after a summer simmering in an Atlantic once again running hotter than normal.

Damage this time appears moderate — particularly in comparison to the massive die-off triggered last year by the opposite extreme, a brutal cold snap. The repeated temperature stresses make corals vulnerable to an ever-widening spectrum of diseases — black band, yellow band, red blotch and an assortment of white maladies that come in band, pox and plague.

And if corals manage to endure all that, there is the looming specter of climate change brewing up an increasingly acidic ocean scientists expect will eventually make it difficult for survivors to simply grow their skeletons.

So it’s hard to overstate the challenges facing the U.S. Coral Reef Task Force, a multi-agency, multi-state group that meets this week in Fort Lauderdale to ponder what, if anything, can be done to protect some of the most important and threatened habitats in the world. Reefs off Miami and the Keys may still seem vibrant to tourists, but they pale in comparison to what they were only decades ago. From Florida to Australia, corals have been in seemingly inexorable decline.

One of the few glimmers of hope may be the emerging effort to promote “reef resilience’’ A program being pondered in the Florida Keys National Marine Sanctuary is shifting the focus from simply counting sick or dying corals to doing more to save them.

“What we’re trying to do is help nature help itself,’’ said Chris Bergh, director of coastal and marine resilience for The Nature Conservancy, who coordinates a program that includes federal, state and university researchers as well as environmental and diver groups “What we can do is give coral reefs more time by trying to reduce the stresses we can control. We need to do this as quickly as possible.’’

“Resilience’’ has become the buzzword for what are really a series of broad, ambitious steps many scientists consider critical to buffering the daunting “multiple stressors’’ afflicting corals.

One primary aim is to reduce the long list of direct human impacts — leaky sewage and septic systems in the Keys, errant anchors, snagged fishing lines and lobster traps, and clumsy or clueless divers – through tougher regulations and expanded protected areas, like a new marine reserve being proposed for Biscayne National Park.

Another is to somehow make corals themselves tougher, drawing on the promising progress of cultivating coral. The hope is to boost the sagging reproductive rates of corals and, with cutting-edge genetic research, potentially increase their tolerance by selectively breeding for hardier strains.

Florida’s program, created under a 2004 agreement among the Florida Department of Environmental Protection, the National Oceanic and Atmospheric Administration and Australia’s Great Barrier Reef Marine Park Authority, has pulled together previously fragmented research and restoration efforts and shown promising signs.

Nubs of cultivated staghorn — a large branching coral that once grew in sprawling forests that began crumbling in the 1970s and have nearly disappeared — have grown prodigiously in a network of underwater nurseries from Broward County to the Keys.

Two years ago, “farm-raised” staghorn transplanted to Molasses Reef — a signature snorkeling destination in John Pennekamp Coral Reef State Park — were observed for the first time engaging in the annual coral spawn, spewing small white sacs called gametes that grow baby corals.

Not even the most optimistic supporters envision nursery coral alone restoring reefs to their lush past. Like giant redwood forests, it can take centuries for dense, high-relief reefs to form, new corals growing atop bones of the old. But if resilience efforts can at least slow the decline, it might give corals a shot at naturally adapting to a changing climate and worsening water quality.

That, at least, is the theory and hope.

Scott Donahue, the sanctuary’s chief scientist, acknowledged there are many questions and “no easy answers.’’

“There are challenges to being sort of like a Johnny Appleseed, if you will,’’ he said. “It sort of boils down to this: If we do nothing, we will definitely fail.’’

Given the bleak trends and growing problems, many of them global in scale, the question is whether the battle may already be lost.

“Scientifically, if I am really brutally honest, I think the jury is still out,’’ said Margaret Miller, an ecologist with the National Marine Fisheries Services on Virginia Key, who has led research on staghorn and elkhorn corals, two important reef builders that became the first to be designated as federally threatened in 2006.

“There are certainly sound management decisions we can take,’’ she said. “The problem is, its death by a million cuts.’’

In other words, how many threats can corals be made resilient to?

Abnormally warm seas have triggered persistent bleaching events, prompting stressed-out corals to shed a symbiotic algae that gives them color and life. But the frigid weather of January 2010 left 20 times more coral carnage behind than the five previous steamy summers combined – “undoubtedly the single worst event on record for Florida corals,’’ said Diego Lirman, a professor of marine biology at the University of Miami who led a study on the chilling effects.

The study, published in August, found overall death rates of 11.5 percent, with losses for some species hitting 40 percent. The worst damage also came in shallower zones that had been largely unfazed during warm-water bleaching events.

“Everybody thought before the cold event that patch reefs in Hawk’s channel were the resilient ones, that they were going to be the one that could save the outer reefs,’’ said Ilsa Kuffner, a research ecologist with the U.S. Geological Survey whose work focuses on coral degradation. “All of a sudden, this event comes and wipes out most of those.’’

Because many corals grow so slowly, there’s also no telling how long it might take to adapt to climate or water chemistry changes, said Miller. Her dives over the last month in the Upper Keys suggest it won’t be overnight. She’s found transplanted staghorn coral beginning to pale right along with other stony species.

Gene Shinn, a retired geologist with the U.S. Geological Survey who pioneered studies of coral growth rates off South Florida, said he’s been impressed by the success of coral nurseries, but remains skeptical that resilience efforts can make much of a difference.

There are simply too many pieces of the puzzles missing, said Shinn, who began diving off South Florida as a teenaged spear fisherman and has chronicled the decline with an extraordinary series of photos dating to the late 1950s. One set shows a brain coral the size of Volkswagen in 1959, withering and all but dead by 1998.

His work pointed to heavy influxes of atmospheric dust from Africa as a possible cause, but he also says a whole slew of suspects remain under-examined – mosquito spraying, agricultural and lawn chemicals and development of the Keys, which ramps up the flow of sewage as well as fishing and diving pressure.

And though global warming is now considered the greatest threat to reefs, the biggest die offs in the Keys occurred decades ago when many scientists were predicting global cooling, said Shinn, now a professor at the University of South Florida.

“If the fish are dwindling, you stop fishing,’’ he said. “No one really knows what is killing these things, so what do you stop?’’

Beyond the scientific questions, mounting an effective resilience program faces political and economic hurdles.

Monroe County is about two-thirds through a state-mandated $900 million upgrade of its sewage system, but faces a $300 million gap to complete the work. More state and federal support is uncertain and the deadline, already pushed back once to 2015, may be moved again.

State lawmakers this year tried to push back another deadline for South Florida utilities to stop pumping some 300 million gallons a day of partially treated sewage into the ocean by 2025 and they’re likely to try again next year. Meanwhile, the Florida Department of Environmental Protection is fighting tougher federal efforts to impose stricter water quality standards, and Gov. Rick Scott has campaigned against new regulations.

Still, some scientists see reasons for hope.

Until the cold snap, an annual survey of coral coverage conducted at 37 sites across the Keys since 1996 showed the loss rate slowing, at least in comparison to staggering declines in the 1970s and 1980s. The survey, coordinated by the Florida Fish and Wildlife Conservation Commission, even showed suggested a small uptick in 2009.

Coral loss is also by no means uniform, varying from reef to reef and species to species. Stands of healthy staghorn have been found off Broward and deeper reefs seem healthier, less impacted by bleaching and disease.

And, even under the myriad stresses, some corals continue growing. Kuffner is two years into a project measuring the accretion rates of massive starlet coral, a species that shown more resilience than many others, at four sites from Miami to the Dry Tortugas. Preliminary results show some growth at each spot. The corals in the Tortugas, 70 miles west of Key West and buffered from human impacts, are gaining girth 30 percent faster.

More study is needed, she said, but it certainly suggests there are benefits to cleaning up local problems.

“I don’t think it’s a one-way road to destruction,’’ said Jerry Ault, a professor of marine biology and fisheries at the University of Miami. “I don’t see that at all.’’